1. Field of the Invention
The present invention relates generally to a communications device, and more particularly, to a communications device for communicating by selecting a predetermined antenna from a plurality of antennae.
2. Description of the Related Art
FIG. 4 is a block diagram of a conventional communications system. The conventional communications device 1 comprises a first antenna 2 and a second antenna 3 for transmitting and receiving; a switching circuit 4 for switching the first and second antennae 2, 3; a transmitter circuit 5 for supplying transmission signals to the first and second antennae 2, 3 via the switching circuit 4; a receiver circuit 6 supplied with reception signals received at the first and second antennae 2, 3 via the switching circuit 4; and a signal processing circuit 7 for modulating transmission signals and supplying them to the transmission circuit 5 and at the same time demodulating and outputting reception signals supplied from the receiver circuit 6.
The first antenna 2 comprises an antenna element capable of transmitting and receiving, the antenna element being used as a transmission antenna during transmission and as a reception antenna during reception.
The second antenna element chiefly comprises an antenna element for receiving, the antenna element being used as a reception antenna element during reception. Both the first and second antennae 2, 3 are connected to the switching circuit 4.
FIG. 5 is a block diagram of a conventional connection switching circuit. The connection switching circuit 4 comprises a first switch 11 for selecting one or the other of either antenna 2 or antenna 3 and a second switch 12 for selecting one or the other of either the transmitter circuit 5 or the receiver circuit 6.
The first switch 11 is an antenna selection switch. A first fixed contact t1 is connected to the first antenna 2, a second fixed contact is connected to the second antenna 3 and a moving contact t3 is connected to the second switch 12.
The moving contact t3 of the first switch 11 is connected to either the first fixed contact t1 or the second fixed contact t2 according to an antenna selection signal supplied from the signal processing circuit 7. When the antenna selection signal supplied by the signal processing circuit 7 is HIGH the moving contact t3 is connected to the first fixed contact t1; when the antenna selection signal supplied by the signal processing circuit 7 is LOW the moving contact t3 is connected to the second fixed contact t2.
The second switch 12 controls the switching between transmission and reception. A first fixed contact t11 is connected to the transmitter circuit 5, a second fixed contact t12 is connected to the receiver circuit 6 and a moving contact t13 is connected to the moving contact t3 of the first switch 11.
The moving contact t13 of the second switch 12 is connected to either the first fixed contact t11 or the second fixed contact t12 according to a transmission-reception switching control signal supplied from the signal processing circuit 7. When the transmission-reception switching control signal supplied by the signal processing circuit 7 is HIGH the moving contact t13 is connected to the first fixed contact t11; when the transmission-reception switching control signal supplied by the signal processing circuit 7 is LOW the moving contact t13 is connected to the second fixed contact t12.
The transmission circuit 5 comprises a power amplifier 21 and amplifies transmission signals generated by the signal processing circuit 7. It should be noted that the transmitter circuit 5 does not in fact comprise only the power amplifier 21 but also includes other circuits as well.
The receiver circuit 6 comprises a low-noise amplifier 22, and amplifies reception signals received by the first antenna 2 and the second antenna 3 and supplies them to the signal processing circuit 7. It should be noted that the receiver circuit 6 does not in fact comprise only the low-noise amplifier 22 but also includes other circuits as well.
A description will now be given of the signal processing circuit 7 with reference once more to FIG. 4.
As shown in FIG. 4, the signal processing circuit 7 has a transmission signal input terminal Ttx for inputting transmission signals; a reception signal output terminal Trx for outputting reception signals; a transmission enable signal input terminal Ttx-en to which is input a transmission enable signal for switching a processing mode of the signal processing circuit 7 to the transmit mode; and a reception enable signal input terminal Trx-en to which is input a reception enable signal for switching the signal processing mode of the signal processing circuit 7 to the receive mode.
When a signal is transmitted, the transmission enable signal input to the transmission enable signal input terminal Ttx-en is HIGH and the reception enable signal supplied to the reception enable signal input terminal Trx-en is LOW. As a result, the signal processing circuit 7 processing mode switches to the transmission mode, the transmission signal supplied to the transmission signal input terminal Tx is modulated and the modulated signal supplied to the connection switching circuit 4. Additionally, the signal processing circuit 7 sets the transmission-reception switching control signal supplied to the first switch 11 of the connection switching circuit 4 or the antenna selection signal supplied to the second switch 12 of the connection switching circuit 4 to HIGH.
Additionally, when a signal is received, the transmission enable signal supplied to the transmission enable signal input terminal Ttx-en is LOW and the reception enable signal supplied to the reception enable signal input terminal Trx-en is HIGH. As a result, the signal processing circuit 7 processing mode switches to receive mode, the reception signal supplied from the receiver circuit 6 is demodulated and the demodulated signal output from the reception signal output terminal Trx. Additionally, the signal processing circuit 7 sets the antenna switching control signal supplied to the first switch 11 of the switching control circuit 4 to LOW and sets the transmission-reception switching signal supplied to the second switch 12 to either HIGH or LOW depending on the quality of the reception signals supplied from the first and second antennae 2, 3.
If, for example, the quality of the reception signals received at the first antenna 2 is better than the quality of the reception signals received at the second antenna 3, then the signal processing circuit 7 sets the antenna selection signal sent to the first switch 11 to HIGH. With the antenna selection signal supplied from the signal processing circuit 7 at HIGH, the moving contact t3 of the first switch 11 is connected to the first fixed contact t1, thus connecting the first antenna 2 to the receiver circuit 6 and supplying the reception signals received at the first antenna 2 to the signal processing circuit 7.
Additionally, if the quality of the reception signals received at the first antenna 2 is worse than the quality of the reception signals received at the second antenna 3, then the signal processing circuit 7 sets the antenna selection signal sent to the first switch 11 to LOW. With the antenna selection signal supplied from the signal processing circuit 7 at LOW, the moving contact t3 of the first switch 11 is connected to the second fixed contact t2, thus connecting the second antenna 3 to the receiver circuit 6 and supplying the reception signals received at the second antenna 3 to the signal processing circuit 7.
However, in the conventional communications device the second switch 12 for switching between transmission and reception and the first switch 11 for selecting either the first or second antenna are connected in series between the first and second antennae 2, 3 on the one hand and the transmitter circuit 5 and receiver circuit 6 on the other. As a result, the transmission and reception signals must pass through both the first and second switches 11, 12 and thus the signals are attenuated by having to pass through two switches.
FIG. 6 is a diagram describing the attenuation in transmission and reception signals caused by the first and second switches when transmitting and receiving conventionally. The conventional communications circuit 1 has connected the first and second switches 11, 12 in series between the first and second antennae 2, 3, on the one hand, and the transmitter circuit 5 and receiver circuit 6, on the other, and as a result signals were attenuated by both the first switch 11 and the second switch 12 when either transmitting or receiving.
It is possible to increase the amplitude of the signals at the transmitter circuit 5 and the receiver circuit 6 in order to offset the attenuation of the signals by the first and second switches. However, increasing the amplitude of the signals also results in increased power consumption.
Accordingly, it is an object of the present invention to provide a communications device capable of reducing signal attenuation during transmission and reception.
The above-described objects of the present invention are achieved by a communications device comprising:
a plurality of antennae;
a first means for communicating by using a predetermined antenna selected from the plurality of antennae;
a second means for communicating by using one of the plurality of antennae;
a first switch for connecting the predetermined antenna of a plurality of antennae to either the first communicating means or the second communicating means; and
a second switch for connecting the second communicating means either to the first switch or to an antenna out of the plurality of antennae other than the predetermined antenna.
According to the invention described above, by connecting the first communicating means to the predetermined antenna via only the first switch when communicating by using the first communicating means, or when using an antenna other than the predetermined antenna used when communicating by using the first communicating means of a plurality of antennae when communicating by using the second communicating means, the signal is attenuated only by the second switch, and thus signal attenuation can be reduced as compared to the conventional arrangement.
Additionally, the above-described object of the present invention is also achieved by the communications device described above further comprising a first control means for controlling the first switch so that the predetermined antenna is connected to the first communicating means when the first communicating means is used for communication and the predetermined antenna is connected to the second switch when the second communicating means is used for communicating.
According to the invention described above, by controlling the first switch using a first control means, the first switch can be automatically controlled.
Additionally, the above-described object of the present invention is also achieved by the communications device as described above further comprising a second control means for controlling the second switch so that the second communicating means is connected either to the first switch or to an antenna out of the plurality of antennae other than the predetermined antenna when the second communicating means is used for communicating.
According to the invention described above, by controlling the second switch by using a second control means, the second switch can be automatically controlled.
Additionally, the above-described object of the present invention is also achieved by the communications device as described above, wherein the predetermined antenna comprises a dual transmission-reception antenna, with the first communicating means performing transmission and the second communicating means performing reception.
Additionally, the above-described object of the present invention is also achieved by the communications device as described above, wherein the first switch is connected between the predetermined antenna and the first and second communication means and the second switch is connected between the second communicating means and the first switch and an antenna out of a plurality of antennae other than the predetermined antenna.
According to the invention described above, the first communicating means can be connected to the dual transmission-reception antenna via only the first switch when transmitting using the first communicating means, and thus signal attenuation can be reduced. Additionally, for reception as well, the second communicating means can be connected to the dual transmission-reception antenna via only the second switch when receiving using an antenna other than the predetermined antenna and the second communicating means, and thus signal attenuation during reception can be reduced.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.